**ABO incompatibility happens when antibodies recognize A or B markers on another person's red blood cells as foreign and attack them.**
Your inherited blood type determines which A and B markers your red blood cells carry. If you receive incompatible donor red blood cells, your antibodies can destroy them, which is why your care team checks compatibility before a transfusion. During pregnancy, some antibodies can cross the placenta and break down your baby's red blood cells if your blood types are incompatible. A pregnancy mismatch does not always cause illness, but it can cause newborn jaundice or anemia. Keep your prenatal testing and newborn follow-up appointments so your clinician can identify problems early.
Why ABO incompatibility happens
Common questions
Why does ABO incompatibility happen?
ABO incompatibility happens because antibodies react to unfamiliar A or B markers on red blood cells. Your blood type is inherited; for example, if you have type A blood, you normally have antibodies against type B. Incompatible donor red blood cells can trigger their attack during a transfusion. During pregnancy, antibodies crossing the placenta can also attack your baby's incompatible red blood cells, causing jaundice or anemia. A mismatch alone does not mean your baby is ill. Your clinician uses blood tests to check compatibility and whether red blood cells are breaking down.